1. Field of the Invention
The invention relates to cross-flow filtration. In general terms, the filter and method of filtration of the invention can be used for the removal of suspended matter of any size, i.e., having dimensions of sand grains or less, and the invention could be used for instance for dewatering or concentrating dredge spoil prior to dumping (not necessarily with a membrane on the filter support). However, the invention is preferably used for the particle sizes associated with micro-filtration or smaller, i.e. sizes associated with micro-filtration, ultra-filtration or reverse osmosis. The minimum retained particle sizes for micro-filtration and ultra-filtration may be considered to be very roughly 10.sup.-7 to 10.sup.-8 m (colloidal range) and 10.sup.-8 to 10.sup.-9 m (macromolecular range), respectively. Colloidal particles and suspended liquids such as oil could be held back. More particularly the filter and method of filtration of the invention are useful for treatment of wastewater, both industrial and domestic.
2. Related Art
Cross-flow filters are known, and comprise a filter support, which may form or merely support the actual filter material or (dynamic) membrane; the filter membrane may be formed by material circulated across the filter support before the feed is applied or may be formed by the feed itself, either as an inherent ingredient of the feed or as an additive to the feed. The membrane is often referred to as a pre-coat in microfiltration and as a gel coat in reverse osmosis. The filters also comprise an inlet for feed which is led to the filter membrane, an outlet for permeate which has passed through the filter membrane, and an outlet for concentrate which is not passed through the filter membrane; the outlet for concentrate will be arranged to ensure back pressure and may have a specific back pressure valve. The feed passes under pressure along the surface of the filter membrane and causes turbulence to occur adjacent to the filter membrane. Periodic cleaning is required, but the filter operates continuously for long periods; once an initial layer of retained material has been deposited on the filter support to form the membrane, the turbulence provided inhibits further deposition--thus cake build up is minimised and a good flow (flux) through the filter membrane is maintained. Although the cleaning of the filter membrane is not very frequent, it is important that the filter support should provide for effective cleaning and the removal of matter which tends to block the interstices or pores of the filter support and gradually reduce the efficacy of the filter. It is found that it is difficult, unless elaborate cleaning methods or systems are used, to dislodge such matter from effectively rigid filter media or from relatively thick filter media such as fire hose carcass material, into which matter penetrates deeply before retention.
In unpublished experimental work carried out by George Raymond Groves, a number of side-by-side fire hoses extended horizontally between the two spaced, horizontal beams. The material of the fire hoses was relatively inflexible. To clean by back-flushing, the lengths of hoses were moved past stationary jets by winding the hoses from one beam to the other. The fire hoses were cumbersome to handle when setting up the equipment, and the hose material gradually blocked up due to inadequate cleaning when back-flushing.